During taxi an aircraft uses a ground propulsion system to control the speed and torque of landing gear axels and wheels. Typically, aircraft engines are used for propulsion power. However, using the aircraft engines for taxi is inefficient and poses safety risk to ground personal. Alternatively, a towbar/wheel tug can be used. However, the use of a towbar/wheel tug for push back and maneuvering creates a dependence on ground support personal and equipment. Additionally, the aircraft must carry additional weight in the towbar when operating between remote runways. The towbars can weigh up to several hundreds of pounds.
Another alternative is the use of one or more high powered electric motors to propel the aircraft for taxi. These electric motors require liquid jacket cooling to avoid exceeding the maximum temperature of the motor. However, the coolant used for cooling the motors can freeze during flight due to low ambient temperature in a landing bay area. Additionally, routing coolant lines through a folding landing gear is difficult. Furthermore, the use of electric motors requires the use of inverters, rectifiers and amplifiers to vary the motor speed. These devices also require cooling.